Commercial wear resistant Stellite alloys are derived from the Co—Cr—W—C family first investigated by Elwood Haynes in early 1900s. Hardfacing alloys of the Co—Cr—W—C type exist in several modifications, and it is generally known that the available range of commercial grades satisfies most industry requirements. However, the high carbon Co—Cr—W—C alloys may occasionally be inadequate especially where components of pumps, impellers, etc., must often withstand the simultaneous abrasive and corrosive action of media composed of a suspension of hard mineral particles in aqueous solution. Such failures are encountered, for instance, in the superphosphate industry.
The Co—Cr—Mo—C type Stellite 700 series alloys developed at Kennametal Stellite, Inc. raise the standards for wear and corrosion resistant alloys. These Stellite alloys have the unusual combination of excellent wear resistance and exceptional corrosion resistance in environments that are either reducing or complex. Co-based Stellite alloys such as Stellite 720 with nominal composition of Co-33Cr-18Mo-2.45C are known for their excellent wear and corrosion resistance. Accordingly, Stellite 720 alloy can be used as a coating applied in the green state by slurry or cloth processes, such as the UltraFlex and Conforma Clad technologies offered by Kennametal, Inc. The green coating is subsequently sintered to fuse the coating into a dense, uniform layer metallurgically bonded to the substrate. However, Stellite 720 is difficult to apply by thermal spraying techniques, such as high velocity oxygen fuel (HVOF). Further complicating coating adherence is the general concept that thickness limitations exists for spraying various coating compositions on a given substrate. Therefore, the wear resistant and corrosion resistant properties of Co—Cr—Mo—C type alloys remain largely unrealized for thermal spray applications.